The objective of this study is to propose more effective measures to improve the drainage capacityin the Bac Hung Hai irrigation and drainage system, which is in the Red river delta of northern Vietnam. First, Cunge's method developed for a looped network is reviewed, and a more time-saving calculation procedure is proposed. In the proposed procedure, the number of unknowns is reduced in advance, because the CPU time consumed for the matrix calculation is proportional to the 2nd to 3rd power of the number of unknowns. Therefore, this procedure is useful for solving a simultaneous linear equation system having a large number of unknowns. Second, the Bac Hung Hai area is modeled as an open channel network composed of numerous drainage channels, paddy fields, and pumps. Parameters of the model are identified through the calibration and the verification processes using two types of hydrological data for ten days in 1994 and in 1985. Using this model, more effective measures are sought with the aim of reducing damage caused by a heavy rainfall having 1/10 exceedance probability. Four feasible measures are tested to compare their effectiveness: (1) widening outlet sluices, (2) canal dredging, (3) dredging and construction of major pumping stations, and (4) dredging and installation of minor inner pumps. To calculate the area damaged by flooding, the Vietnam standard is employed, in which a flooded paddy field is such that the water depth remains more than 287 mm for more than 24 hours. Through the examination, measure (1) turns out to have no effect, but measures (3) and (4) have remarkable effects if pumping capacities are adequate.

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In this paper, an attempt has been made to present an overview of irrigation and water management practices in India. First the geography and climate of India are discussed, and then an outline of Indian agriculture and its progress is given. The status of the renewable water resources of India is described, together with the present and future scenarios of water demands in various sectors. The need for and importance of irrigation in a country like India with its diverse natural conditions is also highlighted, along with the salient features of the major types of irrigation systems prevalent in India. The expansion of irrigation and its effectiveness are succinctly described. Some pertinent aspects of irrigation systems such as water allocation and distribution methods, water pricing, and irrigation management organization are discussed under separate sections. Further, the water management scenario in India and the country's national water policy are briefly presented. Specifically, the status quo of the Bhakra Irrigation System is described as an example of Indian irrigation systems. The paper closes by emphasizing the urgent need to modify the prevailing strategies for water resources management in order to ensure sustainable development.

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Using soil, crop and climate data from three agro-ecological zones of Ghana and rainfall-runoff coefficients from Niger, the authors, show by computer simulation, that tank irrigation offers a sustainable alternative to rainfed agriculture in Ghana. Water balance of rainwater catchment apron, water storage tank and a 350m²-cultivated field is simultaneously carried out bounded by the condition that the tank does not empty during the period of simulation. Suitable apron areas are determined for three crops grown under different climates with sprinkler and drip irrigation. Results indicate that drip irrigation economises on apron area by as much as 41% in the case of citrus, 22% for Tomato and 28% for maize compared to sprinkler. Optimum tank capacities are also economised by over 40%. This is attributed to reduced field evapotranspiration under drip irrigation. Irrigation type makes little difference to apron area under moist conditions, because then, drip behaves similarly to sprinkler irrigation. Small tank capacities produce excessive tank overflows which, are aggravated in sprinkler irrigation. Low rainfall years also force the system to have large apron areas that cause excessive overflow in good rainfall years.

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Colloidal phenomena are concerned with various aspects of solid-liquid separation, mechanical properties of soil containing clay and organic materials, and dynamic change of water quality in rivers, lakes, and estuaries. One of the important and interesting points is that colloidal particles are apt to aggregate, and the state of aggregation is sensitively influenced by the change of ionic strength (effective concentration of ions); and, in accordance with this change, macroscopic behavior of colloidal dispersion changes remarkably. That is, under the condition of low ionic strength, colloidal particles will repel each other by the effect of electrostatic repulsion, and they remain suspended for a long time in the liquid. In contrast, under the condition of high ionic strength, the electrostatic repulsive force will become negligibly small compared with van der Waals attractive force, and through this force the colloidal particles will stick to each other to form big flocs. It is not difficult to find a floc composing of over one hundred million primary particles. In this case, it is important to analyze the system not only in terms of physical chemistry but also from the viewpoint of hydrodynamic process. However, the latter aspect has not been well studied compared to the former even though most practical problems involve dynamics. In our series of investigations, these aspects have been underlined systematically. The whole study can be categorized into three main parts:
(1) To clarify the methodology (way of analysis) using model colloidal suspension.
(2) To confirm the validity of (1) for the analysis of clay colloidal suspension.
(3) To apply the methodology of evaluating the characteristics of blue-green algae.

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A flume with vertical concrete walls is exposed to wintertime weather conditions, and soil backfilled for the wall can reach temperatures below 0°C. A major factor in wall damage is the force of frost heave from backfilled soil, which is a result of the volumetric expansion of moisture as it freezes.
The conventional method of preventing frost heave has been a “replacement” method, i.e., replacing the backfilled soil with pit-run gravel to the maximum frost penetration depth. Replacing soil with gravel serves to prevent frost heave through improved drainage.
In recent years, however, problems have arisen due to the huge amount of soil that must be treated as a byproduct of construction and the considerable increases in the price of gravel. Thus, replacement must be reevaluated because of the high construction cost of the flume.
To this end, the authors attempted use of a “thermal insulation method” to prevent frost heave in backfilled soil by attaching a water-permeable thermal insulator (expanded polystyrene) to the back of the vertical wall. The work also involved measuring the frost penetration depth, observing the behavior of the wall, and investigating the cost efficiency of the method's use.
Use of the thermal insulation method was attempted in 1981 by the Hokkaido Development Board, but it was not employed in the end because of the price of the thermal insulation (polystyrene foam), which was relatively expensive. Furthermore, frost heave was enhanced because of the insulation's impermeability to water.
A thermal insulator that is readily water-permeable was recently developed, and the total cost is expected to be similar to that of the replacement method, thus necessitating subsequent investigation of the thermal insulation method.
Results were satisfactory in that the thermal insulation method inhibits frost in backfilled soil better than the replacing method does, and also relieves frost heave. The results confirmed that this method is superior in cost efficiency, in terms of the reduced cost for replacement material and the cost of treating byproduct soil.
This investigation was designated by the Hokkaido Development Board as a “pilot project for technology application, ” and subsequent deliberation resulted in the new technology being approved for widespread utilization throughout the Hokkaido district.

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The region under our investigation has prospered as a governmental and cultural center for a long time, and has been cultivated for farming since an earlier age. Because of the low precipitation there, many irrigation ponds were constructed to secure the necessary agricultural water. There exist more than 10, 000 ponds, including those made in modern times, and most of them are now being used. However, so many years have passed since the irrigation ponds were constructed that some ponds have lost their impermeability because of percolation from their bank-bodies as the result of wind wave erosion; in other ponds, sands have accumulated on the base as muddy sediments, and their intake facilities have lain buried. These ponds could cause disasters if left as they are. Thus we are executing pond improvement works and advancing government-operated agricultural land disaster prevention project in order to prevent disasters. Our present method of pond improvement, reconstructing bank-bodies with impervious fine-quality soil after digging out the poor sediments on the base and existing bank-body, has several problems:
1) It is difficult to secure a place where fine quality soil can be obtained because of extensive development control, including spots where the cultural properties have been buried, scenic zones, and so on.
2) Gathering of soil could lead to environmental destruction.
3) It is difficult to secure land for filling-up reclamation, where the excavated poor soil can be disposed of.
4) Transport of soil, with its vibration and noise, could worsen environmental pollution.
Pond improvement projects are essentially expected to harmonize with the ecosystem and the natural environment and contribute to creation of amenities and activation of communities. So we have examined a method in which the poor sediments dug out from the bases of ponds and existing bank-bodies are utilized as banking materials in order to realize “preservation of the natural environment, reduction of influence on surroundings, water quality improvement, and water amenity creation in the ponds” as the result of reducing the use of borrow-pits and lands for filling reclamation. Our study began with execution of laboratory and field tests for the purpose of utilizing sediments with moisture content on a base improved with cement-based soil stabilizer as permeable zone materials. The tests revealed that utilization as permeable zone materials was possible, and adoption in practical construction as a new method also showed good results. Our study is at the next stage, of investigating the possibility of utilization as impermeable zone materials. Utilizing poor soil wasted until now, improved with cement-based soil stabilizer as the banking material, we executed the laboratory tests and field test construction, and examined such problems as follows, :
1) Materials: how to secure endurance
2) Structural Mechanics: how to secure imperviousness and strength
3) Constructional Convenience: how to construct effectively and easily
4) Constructional Cost: how to construct expensively compared with other methods

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The 25th session of the FAO Regional Conference for Asia and the Pacific was held in Yokohama from August 28 through September 1, 2000. Thirty-two member countries from the region, representatives of intergovernmental and nongovernmental organizations, media correspondents attended. The broad objective of the Conference was to provide a forum for discussions among Asian and Pacific countries on recent trends in the agricultural and food sectors, food security and rural development. The main outcome of Ministerial-Level Session and Sustainable Agricultural Develop ment and Poverty Alleviation in the New Millennium. Reflections and Lesson from the Asian Crisis is as follow. This report extract from MAFF UPDATE Number 380.

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